1. Field of the Invention
The present invention relates to a driving support apparatus for a vehicle, which is configured to support driving of a driver so that a vehicle travels within a lane.
2. Description of the Related Art
Hitherto, there has been known a driving support apparatus for a vehicle, which is configured to carry out lane keep assist control and lane departure alert control. The lane keep assist control is control for supporting a steering operation of the driver by: detecting left and right white lines of a road with, for example, a camera sensor; setting a target travel line (e.g., a centerline at a center position of the left and right white lines) based on those left and right white lines; and applying a steering assist torque to a steering mechanism so that a travel position of an own vehicle is maintained near the target travel line.
On the other hand, the lane departure alert control is control for supporting the steering operation of the driver by applying a steering assist torque to a steering mechanism when the own vehicle is likely to depart from the travel lane (from the white line) so that the own vehicle does not depart from the travel lane. The lane keep assist control and the lane departure alert control are hereinafter collectively referred to as travel support control.
The driving support apparatus includes a lane keep assist control unit, which is a functional unit configured to carry out the lane keep assist control, and a lane departure alert control unit, which is a functional unit configured to carry out the lane departure alert control. A control mode in which the lane keep assist control unit carries out the lane keep assist control is hereinafter referred to as lane keep assist control mode. A control mode in which the lane departure alert control unit carries out the lane departure alert control is hereinafter referred to as lane departure alert control mode. The driving support apparatus is configured to be able to switch the control mode between the lane keep assist control mode and the lane departure alert control mode depending on the travel position of the vehicle.
The travel support control is different from automatic driving control in that the travel support control is only control of supporting the steering wheel operation of the driver so that the own vehicle does not depart from the target travel line or the travel lane, and is not control of completely eliminating necessity of the steering wheel operation of the driver. Thus, in a driving support apparatus proposed in Japanese Patent Application Laid-open No. 2014-142965, when a no-operation state in which a driver is estimated not to be operating a steering wheel continues while the travel support control is being carried out, hands-off driving handling processing is carried out. The hands-off driving handling processing includes at least one of stop of the application of the steering assist torque to the steering mechanism and notification of causing the driver to pay attention to the hands-off driving.
In general, the presence/absence of the steering wheel operation is determined based on a steering torque detected by a torque sensor provided on a steering shaft. When the steering torque is less than a threshold, it is determined that the steering wheel operation is not being carried out. The driving support apparatus is configured to measure a continuation period (referred to as no-operation state continuation period) in which the steering torque is less than the threshold, determine that the driver is carrying out a hands-off driving when the measured value reaches a set value, and carry out hands-off driving handling processing. The measurement of the no-operation state continuation period and the execution of the hands-off driving handling processing based on the measurement value are carried out by the lane keep assist control unit and the lane departure alert control unit independently of each other.
Incidentally, during the travel support control, the control mode is switched from the lane keep assist control mode to the lane departure alert control mode, or conversely, from the lane departure alert control mode to the lane keep assist control mode. Therefore, when the control mode is switched while the hands-off driving handling processing is being carried out, the control unit to carry out the control mode after the switching starts the count (measurement) of the no-operation state continuation period. In this case, the no-operation state continuation period is counted from an initial value. Thus, while the hands-off driving actually continues, the hands-off driving handling processing is finished when the control mode is switched. In other words, the application of the steering assist torque to the steering mechanism resumes, or the notification of alerting the driver to the hands-off driving is finished during the hands-off driving. Therefore, the hands-off driving handling processing may not be appropriately carried out.